Rapid pre-screening of cervical smears as a method of internal quality control in a cervical screening programme

Performance of rapid prescreening and 100% rapid review as internal quality control methods for cervical cytopathology

BACKGROUND

An objective of quality control for cervical cytopathology is reducing high rates of false-negative results of laboratory tests. Therefore, methods to review smears such as rapid prescreening and 100% rapid review, which have shown better performance detecting false-negative results, have been widely used. The performance of rapid prescreening and the performance of 100% rapid review as internal quality control methods for cervical cytology examinations were evaluated.

METHODS

For 24 months, 9318 conventional cervical cytology smears underwent rapid prescreening and routine screening. The 100% rapid review method was performed for 8244 smears classified as negative during routine screening. Any discordant results underwent detailed review to define the final diagnosis. This was considered the gold standard for evaluating the performance of rapid prescreening and 100% rapid review.

RESULTS

Routine screening showed increases of 13.3% and 11.5% in the detection of abnormal smears with rapid prescreening and 100% rapid review, respectively. The relative percentage variation showed a 38.1% increase in the diagnosis of atypical squamous cells of undetermined significance with routine screening and rapid prescreening and a 12.5% increase in the diagnosis of atypical squamous cells, cannot exclude high-grade squamous intraepithelial lesion with both rapid prescreening and 100% rapid review. Sensitivity rates of rapid prescreening and routine screening were 48.2% and 83.2%, respectively. Sensitivity rates of rapid prescreening and 100% rapid review were 65.7% and 57.8%, respectively, for detecting false-negative results.

CONCLUSIONS

Inclusion of rapid prescreening and/or 100% rapid review improved the diagnostic sensitivity of the cervical cytology examination and reduced false-negative results of routine screening and can provide good quality control.

Rapid prescreen of cervical liquid-based cytology preparations: results of a study in an academic medical center

A rapid prescreening or rapid rescreening method for quality assurance in cervical cytology has been used in Europe and in Canada but has not been accepted in the United States. The rapid prescreen method was tested in a cytology laboratory that serves an academic medical center with a high-risk population for cervical cancer. For a period of 3 months, a tray of 20 sequentially numbered Surepath™ liquid-based preparations, randomly selected from the cervical cytology daily workload, were each prescreened in a random fashion for 1 minute. Experienced cytotechnologists performed the rapid prescreen. Results were recorded as negative, further review needed, or epithelial cell abnormality, category specified. The 20 cervical cytology preparations were then replaced in their same position in the daily workload for routine screening performed by another cytotechnologist. Final interpretation was by a cytopathologist as requested or required by Clinical Laboratory Improvement Amendments of 1988. The rapid prescreen data was tabulated and compared with data for a similar time period using the laboratory's normal quality assurance program. Seven hundred and twelve cases underwent rapid prescreen. Six hundred and forty-two were interpreted as negative. Twenty-six cases were interpreted as low-grade squamous intraepithelial lesion (LGSIL) or higher. Forty-four cases were classified as needing further review. For the 642 negative cases by rapid prescreening, routine screening reported 537 as negative and 105 as either abnormal or needed cytopathologist review. The error rate for the rapid prescreen is 50 of 712 (7.0%); for LGSIL and above 19 of 712 (2.6%). Of the 105 abnormal cases or those submitted for cytopathologist review, 31 were interpreted as atypical squamous cells of undermined significance (ASCUS), 41 cases as reactive/repair, 17 as LGSIL, 4 as unsatisfactory, 1 as atypical squamous cells, cannot rule out high-grade squamous intraepithelial lesion (ASC-H), 8 as the presence of endometrial cells in a women aged >40, 1 as malignant melanoma, and 2 as within normal limits with the presence of Actinomyces. The laboratory's routine quality assurance program selects cases, 10% of initially interpreted negative cases plus any gynecologic cytology on patients with a prior abnormal cervical cytology, or history of cervical epithelial cell abnormality. This quality assurance program averages 29% of cases, 4,045 of a total of 13,767, in 2008. Thirty-seven (0.9%) cases were detected in this rescreen (ASCUS, 16 cases; LGSIL, 13 cases; 1 high-grade squamous intraepithelial lesion; 4 ASC-H; and 3 atypical glandular cells of undetermined significance). Eliminating ASCUS cases, eight significant cases were detected, with an error rate of 0.2%. In this cytology laboratory, the rapid prescreen did not prove as reliable as routine quality assurance program for cervical cytology cases.

Effectiveness of rapid prescreening and 10% rescreening in liquid-based Papanicolaou testing

Although rapid prescreening (RPS) has been shown to be an effective quality control procedure for detecting false-negative conventional Papanicolaou (Pap) tests, RPS has not been widely implemented in the United States. In our laboratory, cytotechnologists performed RPS in 3,567 liquid-based Pap tests: 1,911 SurePath (BD Diagnostics-TriPath, Burlington, NC) preparations that were manually screened and 1,656 ThinPrep Pap tests (Hologic, Bedford, MA) that were imaged using the ThinPrep Imaging System (Hologic). We compared the sensitivity of RPS, 10% rescreening (R-10%), and routine screening (RS). In contrast with previously published findings, we found that RS + RPS did not improve screening sensitivity compared with RS + R-10%. These results support the following hypotheses: (1) Higher baseline RS sensitivity as a result of Pap test diagnoses standardization implemented for quality improvement purposes decreases the performance impact of RPS. (2) R-10% and RPS quality assurance methods detect diagnostic failures caused by different types of cognitive errors.

Quality control in cervicovaginal cytology by cytohistological correlation

OBJECTIVE

Frequent studies attest to the correlation of cytological interpretations with defined histopathological entities. Nevertheless, as part of quality control, cytology laboratories are required to compare Papanicolaou smear reports with those of cervical biopsies to search for discrepancies. We have attempted to determine and categorize the causes of existing discrepancies in our laboratory in order to clarify the source of errors.

METHODS

We reviewed 670 cervical smears that were paired with subsequent punch biopsy or endocervical curettage samples, obtained within 2 months of the cytology, and found out that 60 smear-biopsy pairs were discrepant regarding the diagnosis. These cases were categorized into four error groups after careful re-evaluation of the original smear and biopsy slides.

RESULTS

In 51 (85%) of 60 cervical smear-biopsy pairs with reports that disagreed, the initial diagnoses of both cervical smear and biopsy were confirmed by the review opinion; in these cases, cytology and biopsy 'sampling errors' were responsible for 40 and 11 instances of discrepancy, respectively. Seven cases (11.1%) were discrepant due to 'smear interpretation errors' and consisted of five cases with initial under-diagnosis and two cases with initial over-diagnosis. One case (1.7%) was due to 'screener error'. In another case, discordance was due to cervical 'biopsy interpretation error', with initial over-diagnosis as squamous intraepithelial lesion.

CONCLUSION

In this retrospective study, we determined the causes of cytohistological discrepancies in cervical samples. The main explanation for discrepancy was 'sampling error'.

Does the time of day or weekday affect screening accuracy? A pilot correlation study with cytotechnologist workload and abnormal rate detection using the ThinPrep Imaging System

BACKGROUND

Workload is extensively regulated in gynecologic cytology. However, sensitive monitors of excessive workload are not available.

METHODS

We measured the variation in abnormal (atypical squamous cells [ASC], low-grade squamous intraepithelial lesion [LSIL], and high-grade squamous intraepithelial lesion [HSIL]) rates for 4 cytotechnologists (CTs) among different days of the week and at different times during the day while they were performing primary screening with the ThinPrep Imaging System.

RESULTS

Three of 4 CTs detected significantly less abnormal cases on 1 day of the week than another (1 Monday, 2 Friday). Two of those CTs detected significantly fewer total abnormal cases in the afternoon than in the morning; this was strongly correlated with increased speed in the afternoon and decreased detection of ASC cases. HPV + rates for ASC cases dropped as the abnormal rate dropped. The third CT detected significantly fewer ASC cases in the morning; this was counterbalanced by an increase detection of LSIL cases, suggesting a shift in diagnostic threshold between the AM and PM. The difference in abnormal detection rates between morning and afternoon correlated with a false-negative fraction of 0.96.

CONCLUSIONS

There are significant differences in detection rates of abnormal cases between days of the week and the morning and afternoon. Correlating abnormal rates and workload between the morning and afternoon may represent a sensitive way to detect excessive workload. Because individual CTs may have different responses to workload and no overall pattern emerged, data on their workload and performance need to be tracked individually.

Surrogate indicators of sensitivity in gynecologic cytology: can they be used to improve the measurement of sensitivity in the laboratory?

Background:

Measuring the sensitivity of screening in gynecologic cytology in real life is problematic. However, other quality measures may correlate with sensitivity, including the atypical squamous cells (ASC)/squamous intraepithelial lesion (SIL) ratio. Whether these other measures can function as “surrogate indicators” for sensitivity and improve the assessment of sensitivity in the laboratory is not known.

Materials and Methods:

We compared multiple quality measures with true screening sensitivity in a variety of situations.

Results:

The abnormal rate, ASC rate, and ASC/SIL ratio were all highly correlated (r =.83 or greater) with sensitivity when the overall laboratory sensitivity was low (85%) but became less correlated (.64 or less) or uncorrelated when the screening sensitivity was higher (88% or 95%, respectively). Sensitivity was more highly correlated with the abnormal rate than the ASC/SIL ratio at low screening sensitivity. While thresholds could be set that were highly sensitive and specific for suboptimal screening, these thresholds were often less than one standard deviation away from the mean.

Conclusion:

The correlation of the abnormal rate and the ASC/SIL ratio with sensitivity depends on overall sensitivity. Standards to define minimum screening sensitivity can be defined, but these standards are relatively narrow. These features may limit the utility of these quality measures as surrogates for sensitivity.